Interhemispheric Contrasts of Ocean Heat Content Change Reveals Distinct Fingerprints of Anthropogenic Climate Forcings

Abstract

During recent decades, both greenhouse gases (GHGs) and anthropogenic aerosols (AAs) drove major changes in the Earth's energy imbalance. However, their respective fingerprints in changes to ocean heat content (OHC) have been difficult to isolate and detect when global or hemispheric averages are used. Based on a pattern recognition analysis, we show that AAs drive an interhemispheric asymmetry within the 20°-35° latitude band in historical OHC change due to the southward shift of the atmospheric and ocean circulation system. This forced pattern is distinct from the GHG-induced pattern, which dominates the asymmetry in higher latitudes. Moreover, it is found that this significant aerosol-forced OHC trend pattern can only be captured in analyzed periods of 20 years or longer and including 1975–1990. Using these distinct spatiotemporal characteristics, we show that the fingerprint of aerosol climate forcing in ocean observations can be distinguished from both the stronger GHG-induced signals and internal variability.